The present application relates to probing.
Characterizing the actual performance of high speed integrated circuit based systems requires accurate knowledge of the electrical characteristics of the wafer forming the integrated circuit, characteristics of the integrated circuit itself, characteristics of the package into which the integrated circuit is placed, characteristics of the circuit board or support upon which the integrated circuit is supported, and characteristics of the interconnect structures which interface both the integrated circuit with the package and the package with the circuit board. These electrical characteristics, which are frequently the subject of measurement, include cross-coupling with neighboring lines, spectral dispersion, electrical resonances, and loss by radiation into the surrounding dielectric.
Traditional measuring stations are constructed to support a device under test, such as an integrated circuit board or package, in a horizontal position. This arrangement provides direct physical access to the probing device from only a single side of the package. Simultaneous access to both sides of a circuit board or package is accordingly unavailable in such test structures. Specially constructed mounting cards are sometimes used which not only hold a package but also attempt to provide all connections on the top of the card for physical access to probing. The use of package mounting cards introduce effects into the measurement data which are not due to the package or its interconnects. These effects must, themselves, be determined and either compensated for or modeled into the final analysis of the data. Regardless, of how these effects are handled, they degrade both the efficiency and accuracy of the resulting package electrical characterization.
GigaTest Labs provides a GTL 5050 Probe Station that facilitates probing on opposite sides of a printed circuit board. A calibration substrate is supported in a horizontal orientation by the horizontal support. The probes are supported by the horizontal support and aligned in an opposing relationship with respect to the calibration substrate. Thereafter, the probes are calibrated using the calibration substrate to determine calibration parameters, such as a set of S parameters. The calibration parameters are used in further measurements to calibrate primarily for the effects of the cables and probe so that the characteristics of the device under test can be determined. One of the clamps is then clamped to the horizontal support of the station in a position suitable for testing one side of the circuit board. The horizontal support including the clamped probe is then flipped over. The other clamp is then clamped to the now upper side of the horizontal support of the station in a position suitable for testing the other side of the circuit board. While functional, the significant movement of the probes necessary for positioning and the flipping of the table necessitates long cables, which introduce error into the calibration.